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Controlling home charging costs, help wanted

Discussion in 'Supercharging & Charging Infrastructure' started by MABMAB, Sep 25, 2019.

  1. MABMAB

    MABMAB Member

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    We have solar on a net metering agreement. We have excess generation but a component of our bill is a peak demand charge. We have a Tesla charger at home. For 6 months during the cooler months our non charging peak demand goes way down. If we keep charging the way we have been the electric bill will have an extra $50 charge per month, not a deal breaker. To keep this lower we can charge our model 3 slower. It seems like this has to be manually set up for each charging session? Is there a way to set the car up to charge at a slower rate when at home without pressing buttons every charge session? In other words, can I semi permanently limit charging to 12 or 20 Amps rather than 30 or 48? Thank you
     
  2. gcardona

    gcardona Member

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    You should be able to set a lower current in your Tesla Wall Connector to limit your charge.
     
  3. MABMAB

    MABMAB Member

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    I would rather not open up the charger and run dip switches on and off based upon needs. I'd rather just tell the car and have the car do it with software
     
  4. jmaddr

    jmaddr Member

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    Setting on your charger will for sure limit it. You can set it on the M3, and it will keep a memory of what you set it to. I usually set mine to 32A (down from 48A) and it stays there *until* I visit a supercharger. Then it will change my setting, usually lower so you may want to check it every so often, especially after a SC session.
     
  5. ai4px

    ai4px Wes

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    SmartEVSE from netherlands will allow you to measure current and thus limit the EVSE. It is NOT bidirectional, so you need to put it on the circuit panel side.... I can see putting a CT on the 200amp feeder into your house and setting the car's total usage to say 10kw... any thing the house draws will cause the smart evse to taper the car back below 10kw total. Cheers.
     
  6. MABMAB

    MABMAB Member

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    It will keep a memory of what it is set to? Perhaps I am not doing this correctly as I set it yesterday am and it was back up after work. Now, I did not charge at all, just put the settings down. Perhaps I try to charge after turning settings down?
     
  7. Rocky_H

    Rocky_H Well-Known Member

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    Yes,this is the way it is supposed to work:
    All Tesla vehicles if you manually dial down the current will save an entry in the car's memory for that charging location. When you come back there and charge again later, it will automatically remember and know to use that lower current at that location. But as you say, it will not just show that on the screen if you're not charging. It think it activates when you plug it in, and it's going to do something.

    There are two functions that are geo-tagged like that: the amps and the scheduled charging function. This is very helpful because people may have two common charging places, like home and work, that need different settings. So you may want your home charging location scheduled to start at 1:00 AM, but when you get to work, obviously that's bad, and you want scheduled charging off, so it starts when you plug it in. It will remember those two locations separately. And the same applies for the current level if you dial it down during a charging session somewhere.

    I did say "supposed to". There rarely are times where it can glitch and reset for some reasons, like after a software update, or if the car's GPS position gets confused so it doesn't quite recognize the exact location it is in, etc. But most of the time it Just Works (TM).
     
  8. mociaf9

    mociaf9 Active Member

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    For a once every ~6 months operation, changing the dip-switch settings on the HPWC really shouldn't seem that onerous. It should maybe take all of 5 minutes, including testing and clean-up. And it would be much more foolproof than relying on a software solution that is liable to various types of wonkiness. When the price for the car's software goofing is an added $50 to your electric bill for that month, how many instances of errors are you willing to pay for before your reluctance to tackle the problem through the hardware is overcome?
     
  9. srs5694

    srs5694 Active Member

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    It's not 100% clear what you mean by this. If you mean a Tesla Wall Connector, then I agree with others that adjusting the dip switch to lower its maximum amperage is likely to be the most reliable option, although it's an awkward one, especially if you want to switch back and forth seasonally.

    If, OTOH, you're relying on the Tesla Mobile Connector that came with the car, you might consider installing a third-party EVSE. An EVSE equipped with JuiceNet, such as most JuiceBox EVSEs, and some Clipper Creek and Aerovironment EVSEs, can be programmed to provide less than their maximum possible outputs via a phone app or Web interface. I'm not certain, but I suspect that ChargePoint, OpenEVSE, and perhaps some others can be programmed in a similar way. Investing in such an EVSE might be worthwhile, especially if you can find one at a good price.

    Another option might be to buy an "underpowered" (16A, 24A, or whatever you need) EVSE for this specific purpose. Installing it alongside a Tesla Wall Connector seems wasteful, but if you plan to buy another EV in the not-too-distant future, having two EVSEs might be worthwhile. If you're relying on a Tesla Mobile Connector, or a Wall Connector on a NEMA 14-50 outlet, then you could swap the EVSEs seasonally.

    One more point: Depending on the nature of the peak demand charge, you might be able to get around it by charging at off-peak times, like late at night. You can set scheduled charging pretty easily in the Tesla's UI. This approach has the advantage that you'll be moving your electric demand for charging to off hours, when the demand on the grid is low, and thus reducing the demand on what are likely the most expensive and polluting power sources in your area, which are spun up during peak usage periods. (The fact that you've got solar panels is irrelevant, if they're grid-tied. They produce power whether or not you use it; when you don't use the power, it just goes to your neighbors and reduces their demand on more remote power sources. Thus, your choices about when to charge do affect the demand on those remote sources, either directly or indirectly, even when you have grid-tied solar panels on your house.)
     
  10. MABMAB

    MABMAB Member

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    To clarify, a peak demand charge is based upon the maximum use of power. My tesla wall connecter seems to pull 7 kw @$7/kw, so my demand charge goes up by about 50 a month. Peak use or off peak use time (we are on a TOU plan) does not matter.
     
  11. Rocky_H

    Rocky_H Well-Known Member

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    I think this could have meant something a little different, though. I know what the peak demand charge is, which is based on that instantaneous highest rate of power during the month. The point he may have been referring to is that at various times the other regular electricity uses in your house could be totaling up to 4 or 5kW anyway during those times in the afternoon, when you have a lot of stuff running, plus air conditioning. So even if you were not charging at all, you would still have your peak charge for the month based on 5kW. And you certainly wouldn't want to charge then, where it could go to 5kW + 5kW = 10kW for the total power draw. At least if you run a 5kW charging load late at night, it won't stack on top, and it would keep the peak demand charge near that 5-6kW level instead of much higher if you ran it in daytime with a lot of other loads on.
     

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